Restricting JTextField input to Integers

Question

I know that this question must have been asked and answered a million times  but I just can t find an easy solution  I have a JTextField that is meant to accept only positive integers as input  I need a way to make sure that nothing else gets input here   I already have a keyListener attached to this control  Removing the other code that this listener is there to handle  I have this          txtAnswer addKeyListener new KeyAdapter              Override         public void keyPressed KeyEvent e                 int key   e getKeyCode                    Restrict input to only integers                if  key  lt  96  amp  amp  key  gt  105  e setKeyChar                           As you can see  I m trying to use the the KeyCode to check whether the key just pressed falls within the range of integers  This seems to work  But what I want to do is to simply disregard the entry if it falls outside of this range  The code e setKeyChar     was meant to handle this  but it doesn t work  The code will compile  but it has no visible effect   Can anybody tell me if I am on the right track  What can I replace e setKeyChar     with to make this work  Or am I totally going in the wrong direction   Thanks

User · Answer

When you type  integer numbers to JtextField1 after key release it will go to inside try   for any other character it will throw NumberFormatException  If you set empty string to jTextField1 inside the catch so the user cannot type any other keys except positive numbers because JTextField1 will be cleared for each bad attempt        Fields  int x  JTextField jTextField1      Gui Code Here  private void jTextField1KeyReleased java awt event KeyEvent evt                                                try           x   Integer parseInt jTextField1 getText           catch  NumberFormatException nfe            jTextField1 setText

User · Answer

Do not use a KeyListener for this as you ll miss much including pasting of text  Also a KeyListener is a very low-level construct and as such  should be avoided in Swing applications   The solution has been described many times on SO  Use a DocumentFilter  There are several examples of this on this site  some written by me   For example  using-documentfilter-filterbypass  Also for tutorial help  please look at  Implementing a DocumentFilter   Edit    For instance   import javax swing JOptionPane  import javax swing JPanel  import javax swing JTextField  import javax swing text AttributeSet  import javax swing text BadLocationException  import javax swing text Document  import javax swing text DocumentFilter  import javax swing text PlainDocument   public class DocFilter      public static void main String   args          JTextField textField   new JTextField 10          JPanel panel   new JPanel          panel add textField          PlainDocument doc    PlainDocument  textField getDocument          doc setDocumentFilter new MyIntFilter             JOptionPane showMessageDialog null  panel           class MyIntFilter extends DocumentFilter       Override    public void insertString FilterBypass fb  int offset  String string           AttributeSet attr  throws BadLocationException          Document doc   fb getDocument          StringBuilder sb   new StringBuilder          sb append doc getText 0  doc getLength            sb insert offset  string          if  test sb toString                super insertString fb  offset  string  attr           else               warn the user and don t allow the insert                  private boolean test String text          try            Integer parseInt text            return true          catch  NumberFormatException e             return false                    Override    public void replace FilterBypass fb  int offset  int length  String text           AttributeSet attrs  throws BadLocationException          Document doc   fb getDocument          StringBuilder sb   new StringBuilder          sb append doc getText 0  doc getLength            sb replace offset  offset   length  text          if  test sb toString                super replace fb  offset  length  text  attrs           else               warn the user and don t allow the insert                    Override    public void remove FilterBypass fb  int offset  int length           throws BadLocationException         Document doc   fb getDocument          StringBuilder sb   new StringBuilder          sb append doc getText 0  doc getLength            sb delete offset  offset   length          if  test sb toString                super remove fb  offset  length           else               warn the user and don t allow the insert                   Why is this important    What if the user uses copy and paste to insert data into the text component  A KeyListener can miss this  You appear to be desiring to check that the data can represent an int  What if they enter numeric data that doesn t fit  What if you want to allow the user to later enter double data   In scientific notation

User · Answer

I used to use the Key Listener for this but I failed big time with that approach  Best approach as recommended already is to use a DocumentFilter  Below is a utility method I created for building textfields with only number input  Just beware that it ll also take single     character as well since it s usable for decimal input    public static void installNumberCharacters AbstractDocument document            document setDocumentFilter new DocumentFilter                  Override             public void insertString FilterBypass fb  int offset                      String string  AttributeSet attr                      throws BadLocationException                   try                       if  string equals                                   amp  amp   fb getDocument                                        getText 0  fb getDocument   getLength                                         contains                                 super insertString fb  offset  string  attr                           return                                            Double parseDouble string                       super insertString fb  offset  string  attr                     catch  Exception e                        Toolkit getDefaultToolkit   beep                                                   Override             public void replace FilterBypass fb  int offset  int length                      String text  AttributeSet attrs                      throws BadLocationException                   try                       if  text equals                                   amp  amp   fb getDocument                                        getText 0  fb getDocument   getLength                                         contains                                 super insertString fb  offset  text  attrs                           return                                            Double parseDouble text                       super replace fb  offset  length  text  attrs                     catch  Exception e                        Toolkit getDefaultToolkit   beep

User · Answer

Here s one approach that uses a keylistener but uses the keyChar  instead of the keyCode    http   edenti deis unibo it utils Java-tips Validating 20numerical 20input 20in 20a 20JTextField txt   keyText addKeyListener new KeyAdapter         public void keyTyped KeyEvent e          char c   e getKeyChar          if     c  gt    0    amp  amp   c  lt    9                c    KeyEvent VK BACK SPACE               c    KeyEvent VK DELETE              getToolkit   beep            e consume                          Another approach  which personally I find almost as over-complicated as Swing s JTree model  is to use Formatted Text Fields   http   docs oracle com javase tutorial uiswing components formattedtextfield html

User · Answer

You can also use JFormattedTextField  which is much simpler to use   Example   public static void main String   args        NumberFormat format   NumberFormat getInstance        NumberFormatter formatter   new NumberFormatter format       formatter setValueClass Integer class       formatter setMinimum 0       formatter setMaximum Integer MAX VALUE       formatter setAllowsInvalid false          If you want the value to be committed on each keystroke instead of focus lost     formatter setCommitsOnValidEdit true       JFormattedTextField field   new JFormattedTextField formatter        JOptionPane showMessageDialog null  field           getValue   always returns something valid     System out println field getValue

User · Answer

I can t believe I haven t found this simple solution anywhere on stack overflow yet  it is by far the most useful  Changing the Document or DocumentFilter does not work for JFormattedTextField  Peter Tseng s answer comes very close   NumberFormat longFormat   NumberFormat getIntegerInstance     NumberFormatter numberFormatter   new NumberFormatter longFormat   numberFormatter setValueClass Long class     optional  ensures you will always get a long value numberFormatter setAllowsInvalid false     this is the key   numberFormatter setMinimum 0l     Optional  JFormattedTextField field   new JFormattedTextField numberFormatter

[java] Restricting JTextField input to Integers

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